Integral capacitance (per unit area of electrode) is given by \[K=\frac{Q}{E- E_{Q=0}}\] where Q is the electric charge (per unit area of electrode), E is the potential of the electrode with respect to a reference electrode, and E Q = 0 is the potential at the point of zero charge.
Source:
PAC, 1974, 37, 499. 'Electrochemical nomenclature' on page 509 (https://doi.org/10.1351/pac197437040499)